The invention relates to a method for joining a plurality of workpiece parts, particularly of vehicle body components, as well as to a joining tool.
For checking the quality of the joining points of a workpiece formed of a plurality of workpiece parts, for example, of a vehicle body component, a nondestructive examination, at least in the manner of spot checking, is an absolute necessity. In the field of vehicle body construction, a nondestructive examination of joined workpieces takes place subsequent to the production. For this purpose, a vehicle selected at random is usually removed and is examined manually. However, the joined workpieces or joining points of each vehicle are never all examined, but the nondestructive examination is always only carried out on individual vehicles and at individual joining points.
In the field of vehicle body construction, the use of fiber-reinforced plastic materials is increasing. In contrast to the joining of workpiece parts made of steel, the joining of workpiece parts made of fiber-reinforced plastic is more complex and has higher reject rates. In order to be able to continue to guarantee a high degree of quality, the number of spot checks has to be increased which results in higher cost and is more time consuming.
It is an object of the invention to provide a possibility for examining joined workpieces that can be integrated into the production without high expenditures of cost and time.
This object is achieved by a method for joining a plurality of workpiece parts, particularly of vehicle body components, wherein
a) the workpiece parts are inserted into a joining tool;
b) the workpiece parts in the joining tool are checked for damage;
c) the workpiece parts are joined by the joining tool; and
d) the joined workpiece is checked for damage in the joining tool.
By examining the workpiece parts and the checked workpiece in the joining tool itself, it becomes possible to examine the workpiece parts and the joined workpiece respectively for damage without requiring large expenditures of time. In addition, each of the workpiece parts to be joined and each of the joined workpieces can be examined, so that, in contrast to random-type testing, quality control of the workpieces is clearly improved.
The workpiece parts can be examined just before the joining and the joined workpiece can be examined immediately after the joining, particularly by a testing device provided in the joining tool, so that newly occurring damage will undoubtedly be the result of the joining.
For example, at least one of the plurality of workpiece parts may be made of a fiber-reinforced plastic material, so that the joined workpiece part can gain the advantages of fiber-reinforced plastic material.
When critical damage to one of the workpiece parts or to the joined workpiece was detected, this workpiece part or the joined workpiece is preferably separated out, so that components with excessive damage will be detected as early as possible and will no longer be used. Typical damages in fiber-reinforced plastic caused during the joining are delamination or inter-fiber failures.
In an embodiment, damage to the workpiece parts before the joining is compared with damage to the joined workpiece after the joining; the damage caused by the joining is determined and the joined workpiece is separated out if the damage caused by the joining is critical. As a rule, the workpiece parts used in automobile body construction already have a certain degree of irregularities, for example, as a result of the placing of holes. It is therefore not possible to set an absolute damage limit as critical for the quality control of a joined workpiece. By comparing the damage to the workpiece parts before the joining and the damage to the joined workpiece part, a conclusion can be drawn concerning damage caused by the joining itself, so that this damage can be assessed separately. In this manner, the assessment of the damage caused by the joining will become significantly more differentiated. In this case, a damage is considered to be critical, for example, if the damage caused by the joining exceeds to a critical extent the magnitude of the irregularities before the joining, particularly if the irregularities classified as not critical before the joining has increased more than two-fold as a result of the damage produced by the joining. Particularly the ratio of magnitudes of the irregularities before the joining to the damage after the joining with respect to one another can also be defined as the limit value.
In a further development of the invention, the workpiece parts and/or the joined workpiece are tested by use of air ultrasound, contact ultrasound, acoustic emission, thermography and/or another nondestructive method. These methods have been tested and are known, so that their use is cost-effective.
In an embodiment of the invention, the joining tool has a die and a die plate, the workpiece parts being examined for damage when the die is disposed on the workpiece part, and/or the joined workpiece is examined for damage when the joining tool is completely closed. In this manner, a fully automated and time-saving examination of the workpiece parts and/or of the joined workpiece becomes possible.
In an embodiment, in the case of one-sided joining methods, the workpiece parts can be examined for damage when the die is disposed on one of the workpiece parts or is positioned at a distance of less than 3.0 mm from one of the workpiece parts. In this manner, the workpiece part can also be examined without any contact.
For example, before Step b) a coupling agent between the die and one of the workpiece parts is supplied in an automated manner, whereby the quality of the examination is improved.
After Step d) the coupling agent between the die and the workpiece is preferably removed in an automated manner, so that the joined workpiece will be free of coupling agent residue.
The evaluation as to whether damage is critical can take place in an automated manner, particularly by comparing the samples obtained during the tests with one another and/or with a limit sample, whereby the personal expenditures for the examination and thereby the occurring costs can be considerably reduced. The comparison of the obtained samples with one another or with a limit sample can take place by way of image processing software, in which case the magnitude of the differences between the obtained samples with one another or between the samples and the limit sample can be used for measuring the damage.
In a further development of the invention, the samples obtained during the examination, together with information concerning the final product, such as the chassis number in the case of vehicles, in which the joined workpiece was installed, are stored in a databank. In this manner, it becomes possible to prove the quality of the joined workpiece, in the event of future claims that may be alleged by a buyer.
The object is further achieved by a joining tool for joining a plurality of workpiece parts, particularly workpiece parts made of a fiber-reinforced plastic material, with at least one testing device, which is constructed on a workpiece contact surface of the joining tool and can examine the workpiece to be joined with respect to damages. By use of the joining tool, it also becomes possible to carry out an examination of the workpiece parts and/or of the joined workpiece without additional transport steps of the workpiece parts and/or of the joined workpiece.
The testing device is preferably constructed for the testing by use of air ultrasound, contact ultrasound, acoustic emission and/or another nondestructive method. In particular, the testing device is a phased array ultrasonic probe, permitting the use of known cost-effective and high-quality testing devices.
The joining tool may be a forming tool having a die and a die plate. It may, in particular, be a semi-tubular punch riveter, in which case, the at least one testing device is provided in the die and/or in the die plate, so that a testing of the workpiece parts and/or of the workpiece can take place directly in the production facility.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.